The invention relates to a driving belt for use in a continuously variable transmission comprising two V-shaped pulleys, which driving belt comprises a carrier consisting of two endless band packages lying side by side, on which transverse elements are disposed, wherein each transverse element includes two recesses positioned opposite each other for receiving the band packages, so that a first part of the transverse element extends under said band packages, a second part of the transverse element is positioned between said band packages and a third part of the transverse element extends above said band packages, wherein each recess includes an inside surface facing towards the band package. Such a driving belt is known from EP-A-0 014 013.
In practice it has become apparent that the shape of the inside surface of the recess must meet specific requirements in order to effect a satisfactory operation of the driving belt. Said shape in particular has an influence on the correct operation of the band packages, which form vulnerable parts of the driving belt. They are subjected to a relatively large tensile strain, and also to a substantial, varying flexural strain, which depends on the transmission ratio that has been selected. Said band packages make contact with the aforesaid inside surface, whereby they can also make contact with the inside surface at the location of the aforesaid second part of the transverse element. It is especially for that reason that in practice said inside surface is always a flat surface, which extends in vertical longitudinal direction.
Each time a direction is described in relation to a transverse element, it is assumed that the transverse element occupies an upright position, as is shown in front elevation in FIG. 2. In said figure, the longitudinal direction is the direction perpendicularly to the plane of the figure.
It has become apparent upon testing the strength of the transverse element that the use of relatively small radii has a relatively large negative influence on the strength of the transverse element. The strength of the transverse element furthermore appears to be critical near the aforesaid second part of the transverse element.
The object of the invention is to improve with regard to the shape of the transverse element, which benefits the strength of said transverse element.
According to the invention, in order to accomplish that objective, the portion of the inside surface that is formed by said second part of the transverse element includes an acute angle (a), near the underside of the band packages, with the plane in which the band packages lie.
In particular when measures are taken to retain the band packages correctly in position during operation of the driving belt, any contact that may take place especially between in particular the lowermost band of a band package and the inside surface at the location of the second part of the transverse element appears to involve little force, so that the risk of damage is small. The band packages can be retained in position, in particular during operation, in that the inside surface is designed to be slightly convex at the location of said first part of the transverse element.
By designing the flat part of the inside surface with a smaller surface area at the location of the second part of the transverse element, which is the object of the aforesaid measure, or even forming the relevant part of the inside surface with a curvature in its entirety, larger radii can be used for the rounding of the inside surface near the second part of the transverse element.
Preferably, said angle (a) is less than 85xc2x0, more preferably less than 75xc2x0 and even more preferably less than 60xc2x0. Also an angle (a) of less than 45xc2x0 can be used advantageously.
In one preferred embodiment, the portion of the inside surface that is formed by the second part of the transverse element includes a substantially flat part, whose length (height) is smaller than the thickness of a band package. Furthermore, the portion of the inside surface that is formed by said second part of the transverse element may exhibit a concave curvature over its entire area.
Preferably, the radius of curvature of the concave portion of the inside surface at the transition between said first and said second part of the transverse element is more than one third, preferably more than half, of the smallest distance between the portion of the inside surface that is formed by the first part of the transverse element and the portion of the inside surface that is formed by the third part of the transverse element.
In one preferred embodiment the radius (R1) of the concave curvature of the inside surface at the transition between said first part and said second part of the transverse element is more than 0.7 mm, preferably more than 0.9 mm.
In one preferred embodiment the portion of the inside surface that is formed by the first part of the transverse element exhibits a convex curvature having a radius (R2) of more than 0.6 mm, preferably more than 1.5 mm, more preferably more than 2 mm, near the transition to the portion of the inside surface that is formed by the second part of the transverse element. A larger radius has a positive effect on the life of the band packages.
Preferably, the smallest vertical distance (A) of the recess amounts to more than 75% of the largest vertical distance (B) of the recess near the second part of the transverse element, more preferably more than 85%.
In one preferred embodiment the width of a band package is more than 80%, preferably more than 90%, of the largest distance between the surface of the transverse element that can come into contact with the pulley and the second part of the transverse element.
Preferably, the transverse element is made from a strip of material by means of a cutting operation, and the edges of the transverse element have been deburred and/or been rounded by means of a tumbling operation.
The invention furthermore relates to a transverse element for use in a driving belt for a continuously variable transmission comprising two V-shaped pulleys, which transverse element includes two recesses positioned opposite each other for receiving band packages forming a carrier, so that a first part of the transverse element extends under said band packages, a second part of the transverse element is positioned between said band packages and a third part of the transverse element extends above said band packages, wherein each recess includes an inside surface facing towards the band package, wherein the portion of the inside surface that is formed by said second part of the transverse element includes an acute angle (a), near the underside of the band packages, with the plane in which the band packages lie.